Printer apparatus, control method and control program therefor, and computer-readable storage medium containing the control program

ABSTRACT

A printer apparatus terminates printing and discharges paper when an interface is disconnected during a printing process, whereby the next print data is received and is appropriately printed. In particular, when a printer apparatus that selectively uses a plurality of interfaces to receive print data from one of plurality of host units so that the print data can be printed by a single printing mechanism has an error such as interface disconnection during a process for printing print data received via the selected interface, the printer apparatus terminates the printing and discharges paper, whereby when print data is received via another interface and is printed, the printing can be smoothly performed without requiring the user to perform any operation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a printer apparatus that islinked to an external host unit via a predetermined interface and thatprints data received from the host unit on cut-sheet paper, a controlmethod and control program used for the printer apparatus, and acomputer-readable storage medium containing the control program.

[0003] 2. Description of the Related Art

[0004] Conventionally, if a cable for the interface with the host unitis disconnected, in other words, the interface link is broken while theabove printer apparatus (hereinafter also referred to simply as the“printer”) is printing the print data, the printer cannot detect andnotify the situation to the user of the printer. In this situation, theprinter cannot receive the print data (including control commands)during a printing process, and the printer performs the printing ofprint data remaining in a receiving buffer that temporarily stores thereceived print data. In many cases, in the remaining print data, printdata for the last page is not completely printed, and the printer doesnot receive a paper-discharge command to discharge the last page.Accordingly, in many cases, disconnection of the interface cable duringthe printing process causes the printer to terminate printing withoutdischarging the sheet of paper on which the print data for the last pageis printed.

[0005] To solve this defect, conventional types of printers are designedso that, when the printer detects a sheet of paper remaining on apaper-feeding path in the printer, it starts printing after initiallydischarging the remaining sheet. However, depending on the arrangementof a paper-feeding path and paper sensors, it is impossible for aparticular type of printer to distinguish between a state in which asheet of paper remains on the paper-feeding path and a state in which asheet of paper is inserted in a manual feeder unit. Thus, theseparticular types of printers are not designed not to perform the initialdischarging of paper when paper is manually fed for printing.

[0006] As for the conventional printer, a type of construction is knownin which a plurality of interfaces are used to link the printer to aplurality of host units, and print data from the host units can beprinted by a single printing mechanism by switching the interfaces toselect one interface.

[0007] In the above-described construction, if a cable for the interfaceis disconnected, while printing print data received from one host unitvia one interface, the printing is interrupted as described above, andthe sheet of paper on which a portion of the remaining print data forthe last page is printed is not discharged. In this state, in a case inwhich print data is received from another host unit via anotherinterface and is printed, if a normal paper-feeding mode is activated inwhich paper is fed from a paper-feeding cassette, the automaticdischarge of the remaining sheet of paper is initially performed, andthe printer can perform printing without any trouble.

[0008] Nevertheless, when print data from another host unit is printedwhile paper is fed manually by the user, initial discharge of theremaining sheet may not be performed depending on the type of printer.In this case, the remaining sheet for the last page must be dischargedby operating the operation panel of the printer in advance. Otherwise,the user must extract the remaining sheet in the case of a printer thatcannot be instructed to discharge the paper by operating the operationpanel of the printer.

[0009] If the user starts printing in which paper is fed manually by theuser without being aware of the remaining sheet for the last page, theprinting is started from a portion other than the beginning of theremaining sheet, and results in a failure.

SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the present invention to providea printer which prevents the foregoing problems from occurring and inwhich, even if an interface is disconnected while printing is beingperformed, the printer terminates printing and discharges the paper,such that print data which is received after the disconnection hasoccurred can be printed. In particular, when the printer detects anerror such as the disconnection of the interface, while the printer isprinting print data received via one interface, the printerappropriately copes with this situation, and when the printer performsthe printing of print data received via another interface with the paperbeing fed manually by the user, the printer does not require the user toperform initial paper-discharge operations or to extract a remainingsheet of paper as in a conventional type of printer. The printer alsoperforms printing without fail.

[0011] To this end, according to an aspect of the present invention, theforegoing object is achieved through provision of a printer apparatusincluding a detection unit for detecting an interface-disconnectionstate, and a control unit for performing control processing in which,when the detection unit detects the interface-disconnection state duringa printing process, the printing is terminated and paper is discharged.

[0012] According to another aspect of the present invention, theforegoing object is achieved through provision of a method forcontrolling a printer apparatus, including a detection step fordetecting an interface-disconnection state during a printing process,and a control step for performing control processing in which, when thedetection step detects the interface-disconnection state during theprinting process, the printing is terminated and paper is discharged.

[0013] According to another aspect of the present invention, theforegoing object is achieved through provision of a control programreadable by a computer provided in a printer apparatus. The controlprogram includes a detection step for detecting aninterface-disconnection state during a printing process, and a controlstep for performing control processing in which, when the detection stepdetects the interface-disconnection state during the printing process,the printing is terminated and paper is discharged.

[0014] According to another aspect of the present invention, theforegoing object is achieved through provision of a storage mediumcontaining a control program readable by a computer provided in aprinter apparatus. The control program includes a detection step fordetecting an interface-disconnection state, and a control step forperforming control processing in which, when the detection step detectsthe interface-disconnection state during a printing process, theprinting is terminated and paper is discharged.

[0015] According to another aspect of the present invention, theforegoing object is achieved through provision of a printer apparatusincluding a plurality of interfaces by which the printer apparatus islinked to a plurality of host units and which are selectively used sothat print data is received from one of the host units and is printed oncut-sheet paper by a single printing mechanism, a detection unit fordetecting an error state in the selected interface, and a control unitfor performing control processing in which, when the detection unitdetects the error state in the selected interface during the printingprocess, the printing is terminated and the printed paper is discharged.

[0016] According to another aspect of the present invention, theforegoing object is achieved through provision of a method forcontrolling a printer apparatus including a plurality of interfaces bywhich the printer apparatus is linked to a plurality of host units andwhich are selectively used so that print data is received from one ofthe host units and is printed on cut-sheet paper by a single printingmechanism. The method includes a detection step for detecting an errorstate of the selected interface during a printing process, and a controlstep for performing control processing in which, when the detection stepdetects the interface-error state during the printing process, theprinting is terminated and paper is discharged.

[0017] According to another aspect of the present invention, theforegoing object is achieved through provision of a computer-readablestorage medium containing a program for controlling a printer apparatusincluding a plurality of interfaces by which the printer apparatus islinked to a plurality of host units and which are selectively used sothat print data is received from one of the host units and is printed oncut-sheet paper by a single printing mechanism. The program includes adetection step for detecting an error state of the selected interfaceduring a printing process, and a control step for performing controlprocessing in which, when the detection step detects the interface-errorstate during the printing process, the printing is terminated and paperis discharged.

[0018] According to another aspect of the present invention, theforegoing object is achieved through provision of a control programreadable by a computer provided in a printer apparatus including aplurality of interfaces by which the printer apparatus is linked to aplurality of host units and which are selectively used so that printdata is received from one of the host units and is printed on cut-sheetpaper by a single printing mechanism. The control program includes adetection step for detecting an error state of the selected interfaceduring a printing process, and a control step for performing controlprocessing in which, when the detection step detects the interface-errorstate during the printing process, the printing is terminated and paperis discharged.

[0019] Further objects, features and advantages of the present inventionwill become apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a functional block diagram showing a printer apparatusaccording to an embodiment of the present invention;

[0021]FIG. 2 is a flowchart showing a process that controls the printerapparatus shown in FIG. 1 and that includes a process performed when aninterface cable is disconnected while the printer apparatus is printing;

[0022]FIG. 3 is a detailed flowchart showing the step S202 shown in FIG.2 which is performed when the interface cable is for packetcommunication; and

[0023]FIG. 4 is a flowchart showing a process that controls the printerapparatus shown in FIG. 1 and that includes a process performed when aninterface cable is disconnected while the printer apparatus is printing

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] An embodiment of the present invention is described below withreference to the accompanying drawings.

[0025]FIG. 1 is a functional block diagram of a control system in aprinter according to an embodiment of the present invention.

[0026]FIG. 1 shows host units A (100) and B (103) (simply indicated by“HOST A” and “HOST B” in FIG. 1), and a printer 116 according to anembodiment of the present invention. In this embodiment, the printer 116is an ink-jet printer.

[0027] The printer 116 is linked to the host units A and B viainterfaces A (101) and B (104). Each of the interfaces A (101) and B(104) is, for example, a Centronics interface, a USB (universal serialbus) interface, an IEEE 1394 interface for packet communication oranother type of network interface, or a wireless interface using radiowaves or infrared radiation, such as a Bluetooth or IrDA (Infrared DataAssociation) interface.

[0028] The control system in the printer 116 has the followingstructure.

[0029] An interface-A controller 102 and an interface-B controller 105respectively communicate with the host units A (100) and B (103) byperforming processing based the protocols of the interfaces A (101) andB (104).

[0030] In order that the interfaces A (101) and B (104) may be switchedfor selectively using either of them, an interface switching controller106 switches the interface-A controller 102 and the interface-Bcontroller 105 and links either of them to a command analyzer/controller107 and a printer-status notification unit 115 at the subsequent stage.

[0031] The command analyzer/controller 107 analyzes a control command inprint data received from the host unit A (100) or B (103) via theinterface A (101) or B (104) that is selected by the interface switchingcontroller 106, and converts the control command into an engine-controlcommand for controlling a printer engine 117 (printing mechanism unit)to perform operations in accordance with the control command. Theengine-control command is output to an engine controller 108 in theprinter engine 117.

[0032] The command analyzer/controller 107 is specifically formed by acentral processing unit. The command analyzer/controller 107 analyzesthe control command in accordance with a control program stored in therandom access memory (RAM) of a storage unit 118, and controls theprinter 116 in accordance with the result of the analysis. Thecontrolling includes control processes indicated by the flowcharts shownin FIGS. 2 and 3, which will be described later. The RAM of the storageunit 118 corresponds to a computer-readable storage medium containing acontrol program for the printer 116, in which the storage medium and thecontrol program are in accordance with embodiments of the presentinvention.

[0033] The command analyzer/controller 107 uses the RAM of the storageunit 118 as a work area for performing various information processessuch as command analysis. Part of the RAM is used as a receiving bufferfor temporarily storing print data received from the host unit A (100)or B (103).

[0034] The engine controller 108 receives the engine-control commandfrom the command analyzer/controller 107, and performs paper-supply,printing, or paper-discharging operations by controlling anink-discharge-head control unit 109, a head-position control unit 110, apaper-supply control unit 111, a paper-feed control unit 112, and apaper-discharge control unit 113.

[0035] In response to an instruction from the engine controller 108, theink-discharge-head control unit 109 controls a bubble-jet head (notshown) as a recording head to discharge ink by supplying power to theheater of the bubble-jet head.

[0036] The head-position control unit 110 controls the position of thebubble-jet head by using a pulse motor or the like to move a carriage onwhich the bubble-jet head is mounted.

[0037] The paper-supply control unit 111 controls the driving of a motoras a paper-supply-mechanism driver, whereby cutsheet paper is suppliedfrom a paper-supply cassette (not shown) mounted on the printer 116 or amanual paper-supply portion (not shown) of the printer 116.

[0038] The paper-feed control unit 112 controls the driving of a motoras the driver of a paper-feeding mechanism for feeding a supplied sheetof paper in the printer 116, whereby the supplied sheet is fed.

[0039] The paper-discharge control unit 113 performs paper dischargingby controlling the driving of a motor as the driver of a paper-dischargemechanism for discharging a printed sheet from the printer 116.

[0040] A printer-status manager 114 posts, to both the commandanalyzer/controller 107 and a printer-status notification unit 115, thestatus of the printer 116 which is posted from the engine controller108.

[0041] The printer-status notification unit 115 posts the status of theprinter 116 to the host unit A (100) or B (103) via the interfaceswitching controller 106.

[0042] Next, with reference to the flowchart of FIG. 2, a controlprocess by the command analyzer/controller 107 and which is describedbelow. The control process includes a process for coping with a case inwhich an interface cable is disconnected (interface link is broken)while print data being received from the host unit A (100) or B (103)via the interface A (101) or B (104) is being printed in theconstruction in FIG. 1.

[0043] Upon receiving print data from the host unit A (100) or B (103)via the interface A (101) or B (104), the command analyzer/controller107 initiates the process in FIG. 2. In step S200, when detecting apaper-supply command from the received print data, the commandanalyzer/controller 107 transmits a paper-supply command to the enginecontroller 108 instructing it to perform paper-supply operations.

[0044] In step S201, the command analyzer/controller 107 determineswhether a paper-supply error has been posted from the printer engine 117via the printer-status manager 114. If a paper-supply error has beenposted, the command analyzer/controller 107 proceeds to step S208, andinstructs a display unit on an operation panel (not shown) of theprinter 116 to display a notification informing the user of a paper-endstatus. After that, the command analyzer/controller 107 goes back tostep S200, and instructs the engine controller 108 to performpaper-supply operations.

[0045] In step S201, after the command analyzer/controller 107 hasdetermined whether or not the paper-supply error has posted, the commandanalyzer/controller 107 proceeds to step S202, and detects about whetheror not the cable of either the interface A (101) or B (104), which isbeing used, is disconnected (whether link by the interface is broken). Aspecific method for the determination will be described later.

[0046] If the cable is not disconnected, the command analyzer/controller107 proceeds to step S203, and instructs the engine controller 108 toperform printing of print data on paper.

[0047] In step S204, the command analyzer/controller 107 determineswhether printing has terminated in accordance with aprinting-job-terminating command. If the command analyzer/controller 107has determined that the printing is not terminated, the commandanalyzer/controller 107 proceeds to step S205.

[0048] In step S205, the command analyzer/controller 107 determineswhether paper must be fed to form a new page. If the commandanalyzer/controller 107 has determined that paper must be fed to form anew page, the command analyzer/controller 107 instructs the enginecontroller 108 to discharge the printed sheet in step S206, andsubsequently goes back to step S200 for supplying paper again. Afterthat, the command analyzer/controller 107 repeats step S201 and thesubsequent steps.

[0049] In step S205, if the determination result is negative, thecommand analyzer/controller 107 goes back to step S202, and repeats stepS202 and the subsequent steps.

[0050] In step S204, if the command analyzer/controller 107 hasdetermined that printing has terminated, the command analyzer/controller107 instructs the engine controller 108 to discharge the printed sheetin step S207, and terminates the process.

[0051] In step S202, if disconnection of the interface cable which isbeing used is detected, the command analyzer/controller 107 jumps tostep S207, and the printed sheet is discharged with the printingimmediately terminated in order to complete the process. At this time,any print data remaining in the receiving buffer of the storage unit 118is erased.

[0052] However, step S207 may be modified so that, after printing allprint data remaining in the receiving buffer, the printing is terminatedand the printed sheet is discharged.

[0053] According to the above-described control process, when oneinterface is disconnected in process of printing print data received viathe interface, printing of print data received via the interface isterminated and the printed sheet is discharged. This prevents theprinting of print data on a remaining sheet when the print data isreceived via the other interface. In addition, when recognizingdisconnection of one interface, a host unit that corresponds to theinterface terminates printing due to time-out, and regards the printingas error processing. When the interface is linked again, the host unittransmits new print data. Also in this case, the print data can beprinted on a new sheet of paper since the previous sheet does notremain.

[0054] A specific method for detecting the disconnection of theinterface cable in step S202 is described below.

[0055] When a Centronics interface is used as the interface that isbeing used, in step S202, it is determined whether no control commandhas not been received for a predetermined period from the correspondinghost unit via the Centronics interface. If no control command has beenreceived, this situation is regarded as a state in which the interfacecable is disconnected. If a control command has been received, thissituation is regarded as a state in which the interface cable is notdisconnected (connection is broken).

[0056] When a Universal Serial Bus (USB) interface is used as theinterface that is being used, in step S202, it is determined whether theUSB interface is suspended, in other words, whether the positive andnegative data signals of the USB interface have been at high level for aperiod or longer. If the USB interface is suspended, this condition isregarded as a state in which the interface cable is disconnected. Ifnot, such a condition is regarded as a state in which the interfacecable is not disconnected.

[0057] When a packet-communication interface is used as the interfacethat is being used, in step S202, a situation in which packets to bereceived for a predetermined period have not been received for thepredetermined period is regarded as a state in which the interface cableis disconnected. The details of the process in step S202 are shown assteps S2021 to S2024 shown in FIG. 3.

[0058] Referring to FIG. 3, in step S2021, a timer counter (not shown)that measures time intervals for receiving packets is initialized. Instep S2022, it is determined whether packets have been received. If thepackets have been received, this condition is regarded as a state inwhich the interface cable is not disconnected. The process proceeds tostep S203 in FIG. 2. In step S2022, if the packets have not beenreceived, the value of the counter is incremented in step S2033, and instep S2024, it is determined whether the counter value exceeds an upperlimit corresponding to the predetermined period, in other words, whetherthe packets have not been received for the predetermined period orlonger. If the counter value does not exceed the upper limit, theprocess goes back to step S2022, and the subsequent steps are repeatedlyperformed. If the counter value exceeds the upper limit, this conditionis regarded as a state in which the interface cable is disconnected, andthe process proceeds to step S207.

[0059] As described above, in this embodiment, while print data,received from either of the host units A (100) and B (103) via either ofthe interfaces A (101) and B (104), is being printed, when disconnectionof the interface cable is detected, the printing is terminated and theprinted paper is discharged. Accordingly, when print data, received fromthe other host unit via the other interface, is printed in amanual-feeding mode, no paper remains in the in-apparatus paper-feedingpath since even the last page at the termination of the printing hasalready been discharged. Therefore, differently from a conventionalcase, it is not necessary for the user to perform operations fordischarging the remaining paper before manually feeding paper, or toextract the remaining paper. In addition, a possibility is eliminatedthat printing may fail due to the next printing initiated from part ofthe remaining paper since the user fails to notice the remaining paper,so that the printing can be performed without fail.

[0060] Upon detecting the disconnection of the interface cable that isbeing used, the command analyzer/controller 107 performs controlprocessing in which printing is unconditionally terminated and theprinted paper is discharged, as described above. However, in accordancewith the type of paper for printing, the command analyzer/controller 107may determine whether to perform control processing on the terminationof printing and paper discharging in accordance with the disconnectionof the interface cable. For example, in a case in which the type ofpaper for printing is expensive special paper, if the paper isdischarged in the middle of printing, and cannot be used for printing,the paper cost increases. Accordingly, the command analyzer/controller107 is not allowed to perform the control processing on the terminationof printing and paper discharging in accordance with the disconnectionof the interface cable. In this case, the printing remains interruptedin accordance with the disconnection of the interface cable, and theprinting of print data received via another interface is prohibited,whereby paper is not uselessly consumed since the disconnected interfacecable is linked again for restarting printing.

[0061] In response to a specified control command received from eitherhost unit, or in response to a specified input from an operation unit(not shown) of the printer 116, the command analyzer/controller 107 maydetermine to perform the control processing on the termination ofprinting and paper discharging in accordance with the disconnection ofthe interface cable.

[0062] These can be easily implemented by changing the control programof the command analyzer/controller 107 which is stored in the ROM of thestorage unit 118.

[0063] In the above-described embodiment, the disconnection of theinterface cable (interface link) is a type of interface error. Thus, thedetection of the disconnection of the interface cable in step S202 (FIG.2) may be changed to the detection of an interface error. The controlprocess shown in FIG. 2 can be applied to interface errors other thandisconnection of an interface link. The interface errors other thandisconnection of an interface link include a communication error inwhich, when the interfaces 101 and 104 are wireless interfaces thatperform communication using radio waves and infrared radiation, such asBluetooth and IrDA interfaces, communication cannot be established dueto an excessive communication range and the existence of an obstacle. Inthis case, the error detection in step S202 is performed such that theprinter 116 is notified of error when communication error is detected inthe wireless interface as either the interface 101 or 104, and the errornotification controls the command analyzer/controller 107 to detectinterface error.

Other Embodiments

[0064]FIG. 4 is a flowchart of a control process for a case in which,when one interface is used to perform printing, the interface isdisconnected, and the other interface is used to perform printing byanother user.

[0065] A program corresponding to the control process in FIG. 4 isstored in the ROM of the storage unit 118, and is executed by the CPU ofthe command analyzer/controller 107.

[0066] In step S400, the process determines whether print data isstored. If the process has determined that the print data is stored, theprocess proceeds to step S401. If the process has determined that theprint data is not stored, the process goes back to step S400.

[0067] In step S401, the process determines whether the print data istermination data. If the process has determined that the print data istermination data, the process ends. If the process has determined thatthe predetermined is not termination data, the process proceeds to stepS402.

[0068] In step S402, the process performs printing of the print data forone line, and proceeds to step S403. In step S402, the processdetermines whether paper is supplied before the printing is performed.If no paper is supplied, paper is supplied.

[0069] In step S403, the process determines whether the interface isdisconnected. If the process has determined that the interface is notdisconnected, the process goes back to step S400. If the process hasdetermined that the interface is disconnected, the process proceeds tostep S404.

[0070] In step S404, the process interrupts the printing, discharges thepaper, and goes back to step S400.

[0071] Next, an example of a process for a case in which, when aplurality of users use a plurality of interfaces to perform printing,one interface corresponding to the first user among the users isdisconnected. For printing by the first user, in step S400, the processdetermines whether print data is stored. If the print data is stored,the process proceeds to step S401. In step S401, the process determineswhether the print data is termination data. If the print data istermination data, the process proceeds to “YES” in step S401 fortermination.

[0072] In step S401, if the print data is not termination data, theprocess proceeds to “NO”, the process performs the printing of the printdata for one line. If the present invention is not employed, step S403is skipped, so that the process goes back to step S400. At this time, instep S400, if print data other than the termination data is not receivedand stored, the process proceeds to “NO” for performing step S400 toawait print data, so that the process loops in step S400 unlessreceiving print data. Thus, in a printer in which the present inventionis not employed, incompletely-printed paper remains held in apaper-feeding unit.

[0073] When, in this condition, print data is received via anotherinterface by another user, paper feeding is performed in order to printthe print data for one line. However, because the remaining paper hasremained in a paper-feed path, printing is initiated from part of theremaining paper. Otherwise, when new paper is supplied for new printing,paper jamming occurs which makes it impossible to perform printing.

[0074] In a case in which the present invention is employed, it isdetermined whether the interface cable is disconnected in step S403, andif the interface cable is disconnected, in step S404, printing isinterrupted and paper is discharged, whereby paper used by the firstuser is discharged beforehand, and print data from the next user can beprinted on new paper in step S402. Otherwise, if paper is fed forprinting print data from the next user in step S402, the presentinvention operates so that paper can be fed without paper jammingbecause incompletely-printed paper does not remain held in thepaper-feeding unit.

[0075] As is clear from the foregoing description, according to theforegoing embodiments, in a printer apparatus which are linked to aplurality of host units via a plurality of interfaces and whichselectively uses the interfaces to receive print data from one of thehost units so that the print data is printed on cut-sheet paper by asingle printing mechanism, the printing is terminated when disconnectionof the selected interface or another type of error is detected duringthe printing process, and the paper is discharged. Therefore, whenanother interface which is not disconnected, or which is free of errorother than disconnection, is used to receive print data in order thatprinting is performed in a mode in paper is manually fed, it is notrequired, differently from a conventional printer apparatus, for theuser to initially perform operations for discharging paper remaining ina paper-feed path of the apparatus before manually feeding paper, or toextract the remaining paper. In addition, according to the presentinvention, a preferable effect can be obtained in that, if the nextprinting is initiated from part of the remaining paper, it can becompleted without fail.

[0076] As described above, according to the present invention, if aninterface link is broken during a printing process, by terminating theprinting and discharging paper, subsequently received print data can beappropriately printed.

[0077] While the present invention has been described with reference towhat are presently considered to be the preferred embodiments, it is tobe understood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. A printer apparatus comprising: detection meansfor detecting an interface-disconnection state; and control means forperforming control processing in which, when said detection meansdetects the interface-disconnection state during a printing process, theprinting is terminated and paper is discharged.
 2. A printer apparatusaccording to claim 1 , wherein said printer apparatus is linked to aplurality of host units via a plurality of interfaces, and when saidcontrol means detects the interface-disconnection state while print datafrom one of the host units is being printed, said control means performscontrol processing in which the printing is terminated, the paper isdischarged, and print data is received from another one of theinterfaces and is printed.
 3. A printer apparatus according to claim 1 ,wherein, when said control means detects disconnection of an interfacebeing used during the printing process, said control means performscontrol processing in which the printing is immediately terminated andthe printed paper is discharged.
 4. A printer apparatus according toclaim 1 , further comprising a receiving buffer for storing print datareceived from a host unit to which said printer apparatus is linked,wherein, when said detection means detects the interface-disconnectionstate caused by an interface being used during the printing process,said control means performs control processing in which, after printingall print data remaining in said receiving buffer, the printing isterminated and the printed paper is discharged.
 5. A printer apparatusaccording to claim 1 , wherein said control means determines, inaccordance with the type of paper used for printing, whether or notcontrol processing is performed in response to the detection of theinterface-disconnection state by said detection means.
 6. A printerapparatus according to claim 1 , wherein said control means determines,in accordance with a specified control command received from a host unitto which said printer apparatus is linked, whether or not controlprocessing is performed in response to the detection of theinterface-disconnection state by said detection means.
 7. A printerapparatus according to claim 1 , wherein said control means determines,in accordance with a specified input from an operation unit provided insaid printer apparatus, whether or not control processing is performedin response to the detection of the interface-disconnection state bysaid detection means.
 8. A printer apparatus according to claim 1 ,wherein: a Centronics interface is used; and when no control commandfrom a host unit to which said printer apparatus is linked is receivedvia said Centronics interface during a predetermined period during theprinting process, said detection means regards the situation as a statein which said Centronics interface is disconnected.
 9. A printerapparatus according to claim 1 , wherein: a Universal Serial Businterface is used; and when said Universal Serial Bus interface issuspended during the printing process, said detection means regards thesituation as a state in which said Universal Serial Bus interface isdisconnected.
 10. A printer apparatus according to claim 1 , wherein: apacket-communication interface is used; and when packets to be receivedfor a predetermined period are not received during said predeterminedperiod during the printing process, said detection means regards thesituation as a state in which said packet-communication interface isdisconnected.
 11. A method for controlling a printer apparatus,comprising: a detection step for detecting an interface-disconnectionstate during a printing process; and a control step for performingcontrol processing in which, when said detection step detects theinterface-disconnection state during the printing process, the printingis terminated and paper is discharged.
 12. A method according to claim11 , wherein said printer apparatus is linked to a plurality of hostunits via a plurality of interfaces, and when said control step detectsthe interface-disconnection state while print data from one of the hostunits is being printed, said control step performs control processing inwhich the printing is terminated, the paper is discharged, and printdata is received from another one of the interfaces and is printed. 13.A method according to claim 11 , wherein, when said control step detectsdisconnection of an interface being used during the printing process,said control step performs control processing in which the printing isimmediately terminated and the printed paper is discharged.
 14. A methodaccording to claim 11 , further comprising a receiving buffer forstoring print data received from a host unit to which said printerapparatus is linked, wherein, when said detection step detects theinterface-disconnection state caused by an interface being used duringthe printing process, said control step performs control processing inwhich, after printing all print data remaining in said receiving buffer,the printing is terminated and the printed paper is discharged.
 15. Amethod according to claim 11 , wherein said control step determines, inaccordance with the type of paper used for printing, whether or notcontrol processing is performed in response to the detection of theinterface-disconnection state by said detection step.
 16. A methodaccording to claim 11 , wherein said control step determines, inaccordance with a specified control command received from a host unit towhich said printer apparatus is linked, whether or not controlprocessing is performed in response to the detection of theinterface-disconnection state by said detection step.
 17. A methodaccording to claim 11 , wherein said control step determines, inaccordance with a specified input from an operation unit provided insaid printer apparatus, whether or not control processing is performedin response to the detection of the interface-disconnection state bysaid detection step.
 18. A method according to claim 11 , wherein: aCentronics interface is used; and when no control command from a hostunit to which said printer apparatus is linked is received via saidCentronics interface during a predetermined period during the printingprocess, said detection step regards the situation as a state in whichsaid Centronics interface is disconnected.
 19. A method according toclaim 11 , wherein: a Universal Serial Bus interface is used; and whensaid Universal Serial Bus interface is suspended during the printingprocess, said detection step regards the situation as a state in whichsaid Universal Serial Bus interface is disconnected.
 20. A methodaccording to claim 11 , wherein: a packet-communication interface isused; and when packets to be received for a predetermined period are notreceived during said predetermined period during the printing process,said detection step regards the situation as a state in which saidpacket-communication interface is disconnected.
 21. A control programreadable by a computer provided in a printer apparatus, said controlprogram comprising: a detection step for detecting aninterface-disconnection state during a printing process; and a controlstep for performing control processing in which, when said detectionstep detects the interface-disconnection state during the printingprocess, the printing is terminated and paper is discharged.
 22. Acontrol program according to claim 21 , wherein said printer apparatusis linked to a plurality of host units via a plurality of interfaces,and when said control step detects the interface-disconnection statewhile print data from one of the host units is being printed, saidcontrol step performs control processing in which the printing isterminated, the paper is discharged, and print data is received fromanother one of the interfaces and is printed.
 23. A control programaccording to claim 21 , wherein, when said control step detectsdisconnection of an interface being used during the printing process,said control step performs control processing in which the printing isimmediately terminated and the printed paper is discharged.
 24. Acontrol program according to claim 21 , further comprising a receivingbuffer for storing print data received from a host unit to which saidprinter apparatus is linked, wherein, when said detection step detectsthe interface-disconnection state caused by an interface being usedduring the printing process, said control step performs controlprocessing in which, after printing all print data remaining in saidreceiving buffer, the printing is terminated and the printed paper isdischarged.
 25. A control program according to claim 21 , wherein saidcontrol step determines, in accordance with the type of paper used forprinting, whether or not control processing is performed in response tothe detection of the interface-disconnection state by said detectionstep.
 26. A control program according to claim 21 , wherein said controlstep determines, in accordance with a specified control command receivedfrom a host unit to which said printer apparatus is linked, whether ornot control processing is performed in response to the detection of theinterface-disconnection state by said detection step.
 27. A controlprogram according to claim 21 , wherein said control step determines, inaccordance with a specified input from an operation unit provided insaid printer apparatus, whether or not control processing is performedin response to the detection of the interface-disconnection state bysaid detection step.
 28. A control program according to claim 21 ,wherein: a Centronics interface is used; and when no control commandfrom a host unit to which said printer apparatus is linked is receivedvia said Centronics interface during a predetermined period during theprinting process, said detection step regards the situation as a statein which said Centronics interface is disconnected.
 29. A controlprogram according to claim 21 , wherein: a Universal Serial Businterface is used; and when said Universal Serial Bus interface issuspended during the printing process, said detection step regards thesituation as a state in which said Universal Serial Bus interface isdisconnected.
 30. A control program according to claim 21 , wherein: apacket-communication interface is used; and when packets to be receivedfor a predetermined period are not received during said predeterminedperiod during the printing process, said detection step regards thesituation as a state in which said packet-communication interface isdisconnected.
 31. A storage medium containing a control program readableby a computer provided in a printer apparatus, said control programcomprising: a detection step for detecting an interface-disconnectionstate; and a control step for performing control processing in which,when said detection step detects the interface-disconnection stateduring a printing process, the printing is terminated and paper isdischarged.
 32. A printer apparatus comprising: a plurality ofinterfaces by which said printer apparatus is linked to a plurality ofhost units and which are selectively used so that print data is receivedfrom one of the host units and is printed on cut-sheet paper by a singleprinting mechanism; detection means for detecting an error state in theselected interface; and control means for performing control processingin which, when said detection means detects the error state in theselected interface during the printing process, the printing isterminated and the printed paper is discharged.
 33. A printer apparatusaccording to claim 32 , wherein: the selected interface is a wirelessinterface, and notifies said printer apparatus of an error state whensaid error state occurs; and said detection means detects said errorstate in response to the error-state notification.
 34. A method forcontrolling a printer apparatus including a plurality of interfaces bywhich said printer apparatus is linked to a plurality of host units andwhich are selectively used so that print data is received from one ofthe host units and is printed on cut-sheet paper by a single printingmechanism, said method comprising: a detection step for detecting anerror state of the selected interface during a printing process; and acontrol step for performing control processing in which, when saiddetection step detects the interface-error state during the printingprocess, the printing is terminated and paper is discharged.
 35. Amethod according to claim 34 , wherein: the selected interface is awireless interface, and notifies said printer apparatus of an errorstate when said error state occurs; and said detection step detects saiderror state in response to the error-state notification.
 36. Acomputer-readable storage medium containing a program for controlling aprinter apparatus including a plurality of interfaces by which saidprinter apparatus is linked to a plurality of host units and which areselectively used so that print data is received from one of the hostunits and is printed on cut-sheet paper by a single printing mechanism,said program comprising: a detection step for detecting an error stateof the selected interface during a printing process; and a control stepfor performing control processing in which, when said detection stepdetects the interface-error state during the printing process, theprinting is terminated and paper is discharged.
 37. A computer-readablestorage medium according to claim 36 , wherein: the selected interfaceis a wireless interface, and notifies said printer apparatus of an errorstate when said error state occurs; and said detection step detects saiderror state in response to the error-state notification.
 38. A controlprogram readable by a computer provided in a printer apparatus includinga plurality of interfaces by which said printer apparatus is linked to aplurality of host units and which are selectively used so that printdata is received from one of the host units and is printed on cut-sheetpaper by a single printing mechanism, said control program comprising: adetection step for detecting an error state of the selected interfaceduring a printing process; and a control step for performing controlprocessing in which, when said detection step detects theinterface-error state during the printing process, the printing isterminated and paper is discharged.
 39. A control program according toclaim 38 , wherein: the selected interface is a wireless interface, andnotifies said printer apparatus of an error state when said error stateoccurs; and said detection step detects said error state in response tothe error-state notification.